Well i just set 100 for the fuel BIAS for all phases!

Hi andy maybe when your home you could look into the advanced tab? I just tried it and it doesn't have an effect? Not sure how to work it.

 

you just pick the waypoints from the list and enter your restriction.

it's a little funky because you are not entering a "meet this altitude at this waypoint" restriction but rather, "i will want to change to this altitude after this waypoint". so you have to pick a waypoint one or two ahead of the level you are trying to meet. if you play around with different values in it you'll see what i mean (there are also some lengthy threads about it in the pfpx forums..) in this case it looks like this:

 

 

that results in the pfpx flightplan looking like this:

L151     VIDOK     149   *DES                   18       5.6 /   5.4   02  00:37
L151     PEPUL     149   *DES                   10       5.4 /   5.5   01  00:38
L151     DISIT     149  FL200  262/032   452    12       5.4 /   5.6   02  00:40
L151     TUBSU     149   *DES                    2       5.3 /   5.6   00  00:40
L151     NEDEX     149   *DES                   14       5.3 /   5.6   03  00:43
L151     KIDLI     149  FL150  241/024   420     8       5.2 /   5.7   01  00:44
         *TOD      149  FL150  241/024   420    39       4.5 /   6.5   05  00:49
WILO3B   MID       149   *DES                   12       4.4 /   6.5   02  00:51

which i think is what you are trying to achieve..

 

 

I have a friend who i speak to that flys for Ryanair and i have there SOPs and loads of other things had a wee look through all the DOCS and nothing mentions short hops etc!

 

yeah i suppose that makes sense, the pilot SOP would probably be 'fly the assigned levels you got from dispatch' and the dispatch folks probably have a much more sophisticated program than pfpx to actually determine those numbers and lots of data from their real flights to influence them

 

as dan pointed out, it's a bit of trouble for what is a very small difference in calculations anyway, well within the margin of error you'd expect to have on landing... with the restrictions in place my trip fuel is 6561lbs, without it it is 6440lbs .. thats a block fuel of 10930lbs vs 10809lbs..

 

cheers

-andy crosby

Well i just set 100 for the fuel BIAS for all phases!

100% is probably good.  I think the default in PFPX when released in 2013 was a 103%. I used the fuel evaluator with no weather, straight, and level at FL340 for 1 hour and applied the results I came up with. After several flights. I was unhappy with the results. So now it's just a trial and error method. I have had it as low as 98% and as high as 101% and just about everything in between. Just yesterday I switched from 98% to 99%. So after two years I still don't believe that I have a bias that is acceptable That is one of the reasons I carry 2000 lbs. of extra fuel. I never want to see the message "Using Reserve Fuel."

Andy i done exactly what you done on the screen shot, i then hit compute flight and it doesn't enter those waypoint rest. ? Do i have to press another button or something to take effect?

Michael just remember carry that extra 2000lbs will mean you are heavier and will burn more fuel

I think in general here there is a misunderstanding between final reserve and FMC reserve fuel.

 

The minimum legal amount of fuel that you can land with (for EU-OPS carriers at least) is 30 minutes (holding at 1500ft aal etc etc). In a 737, I'd guesstimate that this is circa 1000kg (I'm sure someone else will provide a more accurate number).

 

What is entered in to the FMC "Reserves" field will vary between airlines, but very rarely will it be this final reserve figure. Most airlines will enter the diversion fuel figure, which will usually consist of final reserve + diversion (i.e. fuel for a go around, divert to alternate etc etc).

 

On a short flight like the one Vernon is describing, with reduced contingency fuel etc (can be as little as 5 minutes under EU-OPS rules), it is entirely possible that you might only have 100kg or so of contingency. Smart airlines tend to use something called "statistical contingency" fuel, which means that having recorded the amount of contingency fuel burnt on a particular route with a particular aircraft type over a number of sectors, reduced contingency fuel may be planned based on those statistics (usually either 95% or 99%, meaning that 95% or 99% of flights have burnt less than that contingency fuel figure). Not necessarily a big saving on short-haul, but on long-haul it could save you hundreds of kilos or even tonnes.

 

There is nothing preventing you from landing with less than diversion fuel at your destination -- but you obviously must be aware that you are now committed to your destination, and you must still land with at least 30 minutes in the tanks. Of course, there is nothing stopping you from going to a closer airfield than your planned alternate if something happens to close your destination!

 

As Vernon points out, simply carrying an extra 500kg "for mum" will in itself incur a fuel burn penalty and cost-conscious (and environmentally-conscious) airlines these days do not generally approve of the practice. Of course, if as PIC you have looked at the situation -- weather, delays etc -- and you feel you need extra fuel over and above that on the OFP, you can take it, but you will generally be asked what it is you need it for when you order it bearing in mind the OFP will generally have been generated with any expected holding etc included. However, if it's a CAVOK day in to a quiet airfield, there is nothing wrong with taking what's on the OFP and no more.

Like i said my FMC reserve is always Diversion fuel + final reserve fuel rounded off to the nearest 100.

 

My SOPs allow 300kg of extra fuel before needing a reason!

Like i said my FMC reserve is always Diversion fuel + final reserve fuel rounded off to the nearest 100.

 

Yes -- so in effect, you have no problem. The margin to your final reserve is not 100kg, it is 1100kg (2100kg - 1000kg final reserve). The reason you enter diversion + final reserve in to the FMC is so that it warns you if it thinks you're going to start burning in to your diversion fuel. But there is no requirement to land with diversion fuel on board at your destination.

 

From a planning point of view, strictly speaking you should use the advanced tab to enter the SID and STAR altitude constraints -- real-world planning software does mostly do this, but PFPX needs some manual intervention. For instance, I normally set the final SID altitude as the initial cruise level and then select the SID end point and "OPT" in the advanced tab, which may require you to add a few hundred kilos extra in some cases depending on the length of the SID -- indeed, this is precisely the reason for the SID truncation programme currently ongoing at LHR (and, I think, LGW).

Only time i take more than needed is when i anticipate flight disruption and arrival delays when the destination forecast indicates conditions approaching limiting values. In these circumstances e.g. LVP in force, cross-winds (steady or gusting) >25kts, thunderstorms at destination (including PROB 40) then i shall consider taking EXTRA fuel.

Nobody likes tankering extra fuel. It is expensive and takes away performance. But if the weather is really rotten at destination and all around, any reserve will be scant.

 

Such was the case for an Avianca 707 many years ago landing at JFK. The route was miserable all along the eastern seaboard, and the airplane was en route from Medellin. Many flights were missing approaches at airports all around the area and holds were issued along the way. By the time those holds ended and before the approach even began, nearly all the reserve fuel was gone. This was despite the fact that the captain ordered an additional 2,000 pounds of fuel than what was in the dispatch and asked to use a longer runway for takeoff.

 

In such cases I guess the flight should just proceed to a nice VFR airport and land safely.

Such was the case for an Avianca 707 many years ago landing at JFK. The route was miserable all along the eastern seaboard, and the airplane was en route from Medellin. Many flights were missing approaches at airports all around the area and holds were issued along the way. By the time those holds ended and before the approach even began, nearly all the reserve fuel was gone. This was despite the fact that the captain ordered an additional 2,000 pounds of fuel than what was in the dispatch and asked to use a longer runway for takeoff.

 

Situations like this were why the idea of a ground stop came into use. Better to hold at the origin while only burning APU fuel rates (or in some cases, just time), than to hold in the air and burn engine fuel rates.

 

Glad you added that on, though. I was about to say the same.

I ask the same thing lol its PFPX that does it

Vernon

On the planning page for a flight you can specify a particular altitude in the Init Altitude/FL box. You don't need to use one of the four options listed in the drop down. Just left click in the box and enter your selected altitude. You can then enter the altitude as either as FL360 or 36000. Either one will work.

 

Make sure that the target speeds for your climb and descent pages in the FMC agree with the speeds shown for climb and descent in PFPX. I have not found a way to change them. So it's either 280/.78 or 330/.79.

I can't see that box michael where do i go? I'm in the advanced tab page?

I can't see that box michael where do i go? I'm in the advanced tab page?

 

It's on the main details page (the first tab, under Aircraft Details -- Altitude/FL capping).

 

However -- I don't know what the climb performance of the NGX is like, but I imagine that if you're light it doesn't take that long to get up to FL410 and heading down to LGW from Glasgow I would have thought you'd have at least a little time in the cruise. If so, and that's the most economical altitude, there's no reason at all why you shouldn't plan it and fly it (or ask to fly it, at least!).

On the route that Andy posted there is no level cap (the SRD says min FL245/max FL660) so go nuts. If you were using one of the other routes via T256 the max is either FL195 or FL245 and so it would be prudent to stick that in the PFPX altitude cap box as described above.

I can't see that box michael where do i go? I'm in the advanced tab page?

Vernon

 

When the program is started a page appears. On that page I click on New above Flight. I don't click on Add Flight....

Your loosing me here!

So is that the reason i can't enter FL200 and FL150 because of the upper airway?

What i'm trying to do is enter the altitude constraints at DISIT and KIDLI